SIGMA ORI (Sigma Orionis). Double stars are among the amateur's favorite targets, Albireo, Mizar always on the list.
Sigma Orionis is one of the few orbiting binaries found in Orion. Component B has an orbit of 158 years and is one of the few components that traces a not-quite-perfect circle.
[5985] sigma Orionis is another interesting multiple star system. The primary component is composed of a blue dwarf, one of the most luminous stars known, and a B-type dwarf. The other component is also composed of two dwarfs, both B-type.
sigma Ori is a terrific multiple star; in binoculars this blue-white star of 4 mag and a 7th mag companion can be resolved; using a small telescope two closer companions of 7th mag and 10th mag are revealed.
The red glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma Orionis.
 See also: Sky, Star, Nebula, Orion, Alnitak
  
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